1. Technical Field
The present invention relates generally to “flip chip” style packaging of integrated circuits. More particularly, the invention relates to a support coating that is applied at the wafer level to support solder contacts in flip chip styled packaging.
2. Background
Numerous conventional packages for integrated circuit (“IC”) devices involve the formation of solder bumps or other suitable contacts directly on an IC die. The die is then typically attached to a suitable substrate, such as a printed circuit board (“PCB”), such that the solder bumps on the die may be surface mounted onto matching contacts on the substrate. Such surface mount devices are often referred to as “flip chip” devices. In order to reduce the costs of packaging in general, it is generally desirable to perform as many of the packaging steps as possible at the wafer level, before a wafer is diced and separated into individual IC devices.
When packaging surface mount devices, it is common to form the solder bumps directly over the I/O contact pads on the die at the wafer level. Such solder bumps are typically reflowed when the die is subsequently attached (e.g., soldered) to a suitable substrate. During the reflow process, the solder bumps typically collapse to form solder joint connections between the substrate and the attached die. The reliability and lifespan of a typical solder joint can depend on a variety of factors, with one common mode of failure being cracking or shearing due to temperature cycling. Because heat is ordinarily generated whenever an IC device is used, the die, substrate, contact pads, solder joints and other nearby components tend to heat up and expand. Solder, substrates and dice can all have different rates of thermal expansion, such that significant stresses are introduced into a solder joint whenever a significant shift in temperature occurs. When continued use of an IC device results in excessive or high variance temperature cycling, the resulting failure of even one affected solder joint connection can render the entire IC device as unreliable or useless.
It has been observed that the reliability of many reflowed solder joints with respect to this mode of failure is dependent on the wetting angle between the solder joint and the die, as well as the total “standoff” or gap between the substrate and the die. Current attempts to optimize this wetting angle and standoff include defining and controlling various parameters, such as the solder bump size, the amount of solder paste placed on the substrate, and the contact pad size, among others. While many of these techniques do generally help to improve the reliability of reflowed solder joints, there is always a desire to provide even more reliable and more cost effective processes for packaging integrated circuit devices.